Taps for cutting threads into the inside walls of an existing bore in a metal mass have long been known. Taps cleaning out the screw threads of a nut or cutting the threads into a nut part have also long been known. U.S. Pat. No. 568,277 issued to Rall shows a tool for cleaning out the threads of a nut. The tool has a series of teeth at the leading section which fit the threads of the nut and thus remove any contamination. However, before the threads is a pilot portion with flutes in it. The leading edge of the flutes however are not blunted.
U.S. Pat. No. 899,916, issued to Smith, shows a tap with threads only in the center third of the tap. At either end are extensive flutes wherein the leading edge of the flute is sharper than the trailing edge. This allows the tap to be reversible. However, the flutes are involved in cutting a nut blank.
U.S. Pat. No. 1,345,425 to Wells and U.S. Pat. No. 5,033,919 to Choe both show a tap having a pilot section preceding cutting teeth. Neither patent shows a form relief section on the leading edge of the pilot.
Overall, a need still exists for a tap which had a section which would properly orient the tap going into a bore in a mass without the pilot cutting into the walls of the bore, seizing, and breaking. This is important when the length of the bore is substantial, especially when the bore is skewed at an angle which is not perpendicular to a planar surface of the mass. Particularly, a need exists for a pilot to have a form relief opposite in orientation than any form relief present at the start of the cutting teeth used to form threads in the interior wall of the bore. Such a tap would be particularly useful when tapping is done by hand instead of by a machine such as a drill press when parallel orientation of boring mechanism and tap can be mechanically maintained.
The following prior disclosures reflect the state of the art of which applicant is aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior information. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
______________________________________ PATENT NO. ISSUE DATE INVENTOR ______________________________________ 83,371 October 27, 1868 Foster 678,814 July 16, 1901 Riggs 1,408,793 March 7, 1922 Anderson & Masters 1,434,870 November 7, 1922 Brubaker, Jr. 1,539,628 May 26, 1925 Bayer 1,543,007 June 23, 1925 Hanson 1,963,542 June 19, 1934 Bergstrom 2,300,310 October 27, 1942 Poeton 3,346,894 October 17, 1967 Lemelson 4,271,554 June 9, 1981 Grenell ______________________________________